Toothbrush with a Flexible Region in the Handle

ABSTRACT

A toothbrush wherein longitudinally between its neck region and the grip handle is a an undulating region of transverse limbs integrally linked by folds with troughs between the limbs, the troughs containing a thermoplastic elastomer material bonded to the plastic material of said limbs with a ShoreA hardness of 60-70. Specific structures and dimensions of limbs and folds are disclosed.

This invention relates to toothbrushes, in particular to toothbrusheshaving a flexible region in their handle.

Toothbrushes generally comprise a head and a grip handle arranged todefine a toothbrush longitudinal direction (not necessarily a straightline) between them, with a neck region longitudinally between the griphandle and the head. Typically toothbrush handles and heads are made ofa hard plastic material such as polypropylene. Tooth-cleaning elementssuch as bristles, e.g. typically filaments made from nylon, are mountedin the head and project in a transverse direction relative to thislongitudinal direction from the head.

It is known to provide toothbrushes with a resiliently flexible regionin their structure to absorb excessive brushing pressures during use andthereby reduce the likelihood of damage to teeth and soft oral tissuessuch as gums resulting from such excessive pressure. U.S. Pat. No.5,054,154 discloses a toothbrush with an elastic segment between itshandle and its head, in the form of widthways cut-outs across thetoothbrush containing an elastic rubbery material. Another known form ofsuch a flexible region is that disclosed in EP-A-0 336 641A being in theform of an S-bend undulating region longitudinally between the head andthe handle, comprising limbs extending in the transverse direction andintegrally linked by folds with troughs between the limbs, andpreferably made more rigid by means of a longitudinal rib through thefolds. A modification of such a region of limbs and folds is disclosedin WO-A-01/43580 in which there is a thermoplastic elastomer material inthe folds between the limbs, and in which the flexibility can becontrolled by a longitudinally moveable slider which intersects thelimbs.

Since these early publications toothbrushes have been sold by thepresent applicant under the trademarks AQUAFRESH™ and DrBEST™incorporating such an undulating region and attempting to optimizeflexibility. The solution adopted in such commercial embodiments hasalways been the incorporation of a longitudinal rib as described inEP-A-0 336 641. Such toothbrushes have also been sold incorporatingadditionally a flexible link between the toothbrush head and the neckregion of the toothbrush, or located in the neck region of thetoothbrush itself. Such toothbrushes are for example disclosed inWO-A-98/37788.

The incorporation of elastomer material parts into toothbrush heads andhandles to modify flexibility and for other purposes is also known. Forexample WO-A-96/28993 discloses an S-bend undulating regionlongitudinally penetrated by an elastomer material core. WO-A-97/25899discloses elastomer segments in the toothbrush head to modifyflexibility and in the handle to enhance grip and for aestheticpurposes. WO-A-98/05241 discloses elastomer-filled grooves in atoothbrush head to modify flexibility. EP-A-1350442 discloses atoothbrush head made flexible by means of an elastomer-containing hinge.U.S. Pat. No. 4,509,28 S discloses a toothbrush handle with an S-bendundulating region.

A problem has been encountered with toothbrushes incorporating such anundulating region, especially such toothbrushes which also include theabove-mentioned flexible link between the toothbrush head and the neckregion of the toothbrush. The problem is that with the prior undulatingregion incorporating the longitudinal rib the stress experienced by thetoothbrush during tooth brushing is not optimally distributed and thetoothbrush is prone to breakage during use. In toothbrushes which alsoinclude a flexible link between the toothbrush head and the neck regionof the toothbrush it has been found that undulating regions of limbs andfolds can be so rigid that the flexible link between the toothbrush headand the neck region can be subject to excessive stress during use,resulting in breakage and shortening of useful life. It is an object ofthe present invention to address these problems. Other objects andadvantages of the present invention will be apparent from the followingdescription.

According to this invention a toothbrush is provided comprising a headand a grip handle integrally made of a plastics material and arrangedalong a head-handle longitudinal direction, with a neck region betweenthe grip handle and the head, with bristles projecting from the head ina transverse direction relative to this longitudinal direction, thetoothbrush having a width direction perpendicular to the longitudinaldirection and to the transverse direction, wherein longitudinallybetween the neck region and the grip handle is an undulating region,comprising limbs extending in the transverse direction and integrallylinked by folds with troughs longitudinally between the limbs, thetroughs between the limbs having a transverse depth direction andcontaining a thermoplastic elastomer material bonded to the plasticsmaterial of said limbs, characterized in that

the thermoplastic elastomer material has a ShoreA hardness of 60-70.

It is inventively found that use of such a thermoplastic elastomermaterial optimizes the resilient flexibility of the undulating region,especially in the proportions referred to herein.

Preferably there are four such limbs.

Preferably the thermoplastic elastomer material occupies at least 60% ofthe depth “D” and at least 60% of the width of at least one, preferablyeach, trough, more preferably 75-90% of the depth “D” and 75-90% of thewidth. Preferably the thermoplastic elastomer material occupies at least60% of the volume of at least one, preferably each, trough, morepreferably 65-80%.

The term “transverse” as used herein includes perpendicular, and refersto a direction at an angle between 45° and 90° to the longitudinaldirection. Preferably the transverse directions, i.e. the direction of aplane midway between longitudinally opposite surfaces of the limb, oflongitudinally adjacent pairs of limbs are aligned at an angle of 0-15°to each other.

Preferably each of the four limbs has a longitudinal thickness “T” of1.2-2.2 mm, and a transversely extending length “L” of 9-13 mm betweentransversely opposite folds, and a width “W” of 9-14 mm in the widthdirection, the four limbs defining longitudinally between longitudinallyadjacent pairs of the limbs three troughs each with a transverse depth“D” of 6-11 mm, a longitudinal breadth “B” of 1-2 mm for at least 60% ofthe lower depth of the trough, each trough containing the thermoplasticelastomer material of ShoreA hardness 60-70 bonded to the plasticmaterial of the limbs between which the trough is situated.

It is inventively found that such alignments, dimensions and proportionsoptimize the resilient flexibility of the undulating region, without anyneed for a longitudinally extending rib penetrating the limbs to modifythe flexibility of the undulating region. Thus in a preferred embodimentof this invention the undulating region does not include alongitudinally extending rib. Such optimization of flexibility isrelative to the ability of the toothbrush to resiliently absorbexcessive toothbrushing pressures whilst also being ergonomically rigidand providing the user with a sense of “feedback” through the handleduring use.

Typically the toothbrush of this invention has a length of 190-200 mmfrom the extreme longitudinal end of its grip handle to the extremeopposite longitudinal end of its head.

Typically the head has a length of 33-35 mm from the point where theneck region begins to widen widthways to form the head to the end of thehead longitudinally furthest from the grip handle.

Typically the grip handle has a length of 105-115 mm from thelongitudinal end of the grip handle remotest from the head to the startof the undulating region.

Typically the undulating region has an overall length of 15-20 mm.

Typically the neck region has a length of 30-40 mm from the end of theundulating region closest to the head to the point where the neck regionbegins to widen widthways to form the head. Typically the neck regionmay have a thickness in the transverse direction of 5.5-3.5 mm, andtypically the thickness may taper, decreasing toward the toothbrushhead. The cross section of the neck region may be any convenient orconventional shape, e.g. semicircular, rectangular (optionally withrounded corners). The neck region may incorporate longitudinal flowchannels to enable elastomer injected at points adjacent the handleduring an injection moulding manufacturing process to flow along theneck toward the head, or vice versa.

Preferably the transverse directions of longitudinally adjacent pairs oflimbs are aligned at an angle of 7-10° to each other. The transversedirections may be parallel to each other.

Preferably as viewed in the longitudinal direction the limbs may have agenerally rectangular (the term includes square) shape, preferably withrounded corners.

In a preferred embodiment the longitudinal thickness “T” of the limbs is1.5-2.0 mm.

In another preferred embodiment the transversely extending length “L” ofthe limbs is 9-12 mm between the extremities of transversely oppositefolds.

In another preferred embodiment the width “W” of the limbs is 9-12 mm inthe width direction. Suitably the width W of the limbs decreases towardthe head of the toothbrush. For example the two limbs closest to thehandle of the toothbrush may have substantially the same width “W”, andthe two limbs closer to the head may be progressively less wide. Suchnarrowing of the width may improve the flexibility of the undulatingregion by concentrating flexibility at the end of the undulating regionclosest to the toothbrush head at which pressure is applied during toothbrushing.

In another preferred embodiment, the depth “D” of the troughs is 6-11mm. For example the three troughs may vary in depth, with thelongitudinally middle of the three troughs being the deepest. In anotherpreferred embodiment the longitudinal breadth “B” of the troughs tapers,narrowing toward the bottom of the trough, and being 1-1.5 mm for atleast 60% of the depth of the trough.

In a preferred embodiment the folds are in the form of an arc of acircle with an outer radius of curvature defining the extremity of thefold of 2.0-2.5 mm, more preferably 2.25-2.35 mm. In a preferredembodiment the thickness of the folds in the radial direction is 1.5-2.0mm. It is found that such a radius of curvature and thickness of thefolds can optimize the flexibility of the undulating region whilstreducing the tendency for the undulating region to break during use.

In a preferred embodiment, at each longitudinal end of the undulatingregion there is an end trough in the plastics material, bounded on onelongitudinal side by an adjacent limb and on the other longitudinal sideby an adjacent surface of the grip handle or head, these end troughsalso containing the thermoplastic elastomer material of ShoreA hardness60-70 and bonded to the plastic material.

Such an end trough can act as a force-absorbing buffer between the neckregion at one longitudinal end of the undulating region, and the griphandle at the other. Preferably such end troughs may have a transversedepth “E” of 5-7 mm, a longitudinal breadth “B” of 1-2 mm for at least60% of the lower depth of the trough. Preferably the thermoplasticelastomer material occupies at least 60% of the transverse depth “D” andat least 60% of the width of each trough.

The neck region is preferably flattened in the transverse direction.Typically the neck region has a thickness “TN” in the transversedirection of 3.5-4.5 mm, for example ca. 4.0 mm. Typically the neckregion has a width in the range 5-10 mm, and typically the neck tapers,narrowing toward the head, for example ca. 9.5 mm wide at its endclosest to the undulating region and ca. 6.0 mm at the point where theneck region begins to widen widthways to form the head. Various crosssectional shapes as cut across the longitudinal direction may be usedfor the neck region, for example rectangular, trapezoidal, semicircular,or such aforementioned shapes cut into by longitudinally extendingmoulding channels for the flow of fluid elastomer material during aninjection moulding process in which thermoplastic elastomer is injectedto form spaced apart thermoplastic elastomer parts of the toothbrush.

In a preferred embodiment the toothbrush of the invention also includesa flexible link situated longitudinally between the undulating regionand the toothbrush head.

Preferably such a flexible link is situated in the neck region therebydividing the neck region into two longitudinally separate parts, one oneach longitudinal side of the flexible link, being a first part closerto the grip handle and a second part closer to the head. The relativelongitudinal proportions of the first part: second part may suitably bein the range 8.5-8.0:1. Such proportions have been found to optimize thedistribution of forces between the flexible undulating region and theflexible link.

Suitably such a flexible link comprises a thinned part, integral withthe neck region, which is transversly and/or widthways thinned relativeto longitudinally immediately adjacent parts of the neck region orrelative to longitudinally immediately adjacent parts of the neck regionand the toothbrush head.

Alternatively such a flexible link may be situated between the neckregion and the toothbrush head. Suitably such a flexible link comprisesa part, integral with the neck region and toothbrush head, which istransversly and/or widthways thinned relative to longitudinallyimmediately adjacent parts of the neck region and toothbrush head.

Preferably the thinned part is in the form of a longitudinally extendingspine of plastics material having a longitudinal dimension of 1-2 mm, awidthways dimension of 2-3 mm, and a transverse dimension of 1.5-2.5 mm.Suitably the cross section of such a spine cut across its longitudinaldirection is circular or oval.

In a preferred embodiment such a spine is surrounded around all of itstransversely- and widthways-facing surfaces by a thermoplastic elastomermaterial, suitably having a spherical shape, suitably with a sphericaldiameter of 6-7 mm. Suitably such a thermoplastic material may be thesame thermoplastic elastomer material that is situated in the troughs,so that the same thermoplastic elastomer material may be used in alllocations. This may be achieved by providing one or more flow channel inthe plastic material of the toothbrush via which thermoplastic elastomermaterial injected at an injection port in an injection mould enclosingthe plastic material part of the toothbrush may flow from one locationto the other. The use of such flow channels to convey thermoplasticelastomer from one location on a toothbrush to another duringmanufacture is conventional in the toothbrush art. Alternativelymultiple injection points may be used to inject the thermoplasticelastomer material into separated positions on the toothbrush.

In a preferred embodiment the end of such a flexible link closest to theundulating region is located within 30 mm of the end of the undulatingregion closest to the undulating region.

When the toothbrush of this invention includes such a flexible link itis preferred that the part of the neck region between the flexible linkand the undulating region (herein the “first part”) is constructed suchthat under the forces encountered during tooth brushing this first partremains rigid relative to the flexibility of the flexible link and theundulating region. For example this may be provided by a first partwhich has a transverse thickness of at least 3.5 mm, preferably at least4 mm, and a widthways width of at least 5 mm, preferably at least 5.5mm. Such a construction helps to transmit force from the toothbrush headto the undulating region during use, so that the undulating region canabsorb much of the forces of toothbrushing and protect the flexible linkwhen present from such forces to thereby reduce the likelihood ofbreakage of the flexible link.

It is found that the above-mentioned dimensions and construction canprovide a toothbrush in which flexibility during tooth brushing isimproved relative to known toothbrushes, and in which the tendency tobreak of a flexible link in the neck region is reduced. It is believedthat this advantage is achieved by means of the above-mentioned S-bendundulating region having an optimized flexibility which spreads stressout along the toothbrush, reducing breaking stress in the region of theflexible link.

Suitable plastic materials for the toothbrush of this invention includethose with a modulus of elasticity of at least about 500 Mpa, preferablyat least about 1000 Mpa, these being conventional in the toothbrush art.Suitable materials include for example, polyamides and polypropylenes.An example of a suitable polyamide is the material Ultramid B3™(marketed by BASF, Federal Republic of Germany), having a modulus ofelasticity (DIN 53452) of 3000. An example of a suitable polypropyleneis the material Novolene 1100 HX™ (marketed by BASF, Federal Republic ofGermany), which is a homopolymer and has a modulus of elasticity (DIN53457) of 1400. Such a polypropylene homopolymer may optionally be usedin admixture with a polypropylene block co-polymer, such as the materialNovolene 2500 HX™ (marketed by BASF, Federal Republic of Germany), forexample in an 80:20 mixture by weight (1100 HX:2500 HX). Other suitablepolypropylenes include Polypropylene PM 1600™ (marketed by Shell) andhaving a modulus of elasticity (ISO 178) of 1500 Mpa and Apryl 3400 MAI™from Elf Atochem, Novolen 2400 H and 1106, and Borealis HG 365 P. Apreferred plastics material is polypropylene, especially thecommercially available polypropylene material 100-GA04 supplied byIneos.

Suitable thermoplastic elastomer materials for the toothbrush of thisinvention include those available under the trade names Megol™ andSantoprene™, and silicone elastomeric materials may also be used. Othersuitable elastomeric polymers include styrene-based thermoplasticelastomers (for example styrene ethylene butadiene styrene, or styrenebutadiene styrene). Preferred thermoplastic elastomer materials are thecommercially available materials TF7 GST and TH7 GSN supplied byKraiburg.

The toothbrush of this invention may be made using a known injectionmoulding process in which the plastics material part of the toothbrushis made in a first stage by injection moulding as an integral singlepart, and including one or more space defining the position and shape ofthe thermoplastic elastomer material part(s) of the toothbrush,including the position and shape of the thermoplastic elastomer materialbetween the limbs. Then in a second stage the so formed plasticsmaterial part is enclosed in a cavity of a second injection mould whichdefines the outer profile of the thermoplastic elastomer part(s) of thetoothbrush, including the shape of the thermoplastic elastomer materialbetween the limbs. Thermoplastic elastomer material is then injectedinto the cavity of this second injection mould to thereby occupy the oneor more space and thereby form the thermoplastic elastomer materialpart(s). Injection of this thermoplastic elastomer material is suitablyunder temperature and pressure conditions such that the thermoplasticelastomer material bonds tightly to the plastics material. Suitabletemperature and pressure conditions are known in the art.

Bristles and/or other oral cleaning elements may be mounted in the headof the toothbrush of this invention in various known, conventional,ways. In one way socket holes may be formed in the plastics material ofthe head of the toothbrush during the first stage of injection moulding,and tufts of bristles may be held in these socket holes using smallmetal collars around the ends of the tufts in a well-known manner. Inanother way the ends of tufts of bristles may be inserted into the partof the cavity of the first injection mould which defines the toothbrushhead, so that plastics material injected into the cavity flows aroundthese ends, and when the plastics material solidifies around the ends ofthe tufts holds the tufts in place.

The toothbrush of this invention will now be described by way of exampleonly with reference to the accompanying drawings.

FIG. 1 shows a view of the plastic material part of a toothbrush of thisinvention looking in the width direction of the plastics material part,without any thermoplastic elastomer present.

FIG. 2 shows a toothbrush of the invention in the same view direction asFIG. 1 with the thermoplastic elastomer present.

FIG. 3 shows a view of the plastic material part of FIG. 1 looking in adirection perpendicular to the longitudinal direction and to the widthdirection, in a transverse direction approximately aligned with thedirection of the bristles.

FIG. 4 shows a view of a toothbrush of FIG. 3 in the same view directionas FIG. 3 with thermoplastic elastomer material present.

FIG. 5 is a longitudinal section of the undulating region of the plasticpart shown in FIG. 1 enlarged to show more clearly the dimensionsreferred to in the description.

Referring to FIGS. 1, 2, 3 and 4, the plastic material part 10 overallof a toothbrush 20 of the invention comprises the plastic part of a head11 and of a grip handle 12 integrally made of a plastics material andarranged along a head-handle longitudinal direction A-A, with a neckregion 13 between the grip handle 12 and the head 11. Holes 14 areformed in head 11 for mounting bristles 15 (shown in FIGS. 2 and 4, notshown in FIGS. 1 and 3) projecting from the head 11 in a transversedirection T-T transverse relative to longitudinal direction A-A. Thetoothbrush 10 has a width direction W-W indicated in the views of FIGS.3 and 4 perpendicular to the longitudinal direction A-A and to thetransverse direction T-T.

Longitudinally between the neck region 13 and the grip handle 12 is anundulating region 16. This region 16 is seen enlarged in FIG. 5 in thesame view direction as FIG. 1. Undulating region 16 comprises four limbs161, 162, 163, 164 extending in a transverse direction TD. Thetransverse direction TD is shown in FIG. 5 for limb 164, being thedirection of a plane midway between the longitudinally opposite surfacesof the limb. Transverse directions of the other limbs 161, 162, 163 areanalogous but are omitted for clarity. The limbs 161, 162, 163 and 164are integrally linked by three folds 171, 172, 173 with a trough 181,182, 183 longitudinally between longitudinally adjacent limbs 161, 162,163, 164.

The toothbrush 20 of this invention has a length of ca. 195 mm from theextreme longitudinal end of its grip handle 12 to the extreme oppositelongitudinal end of its head 11.

The head 11 has a length of ca 34 mm from the point 132 where the neck13 region begins to widen widthways to form the head 11 to the end 111of the head 11 longitudinally furthest from the grip handle 12.

The grip handle 12 has a length of ca. 110 mm from the longitudinal endof the grip handle 12 remotest from the head 11 to the start of theundulating region 16.

The undulating region 16 has an overall length of ca. 17 mm. The neckregion 13 has a length of ca. 35 mm from the end 131 of the neck 13closest to undulating region 16 to the point 132 where the neck region13 begins to widen widthways to form the head 11. The neck region 13 isflattened in its transverse direction B-B. The thickness in thetransverse direction B-B of the neck region is ca. 4.0 mm along itslength, for example the thickness may be ca. 5 mm at the point 131 andca. 4 mm at the point 132. The width of the neck 13 region tapers fromca. 9.5 mm wide at its end at the point 131 closest to the undulatingregion 16 to ca. 6.0 mm at the point 132 where the neck region 13 beginsto widen widthways to form the head 11. The cross section of the neckregion 13 as cut across the longitudinal direction A-A may for examplebe a generally rectangular shape, or for example be semicircular orother cross sectional shapes, and the neck region may includelongitudinal flow channels for elastomer material.

As seen more clearly in FIG. 5, the transverse directions “TD” oflongitudinally adjacent pairs of limbs 161, 162, 163, 164 are aligned atan angle α of 7-10° to each other. As seen more clearly in FIG. 5 thetransverse direction TD of each limb is constructed as the direction ofa plane mid way between the two longitudinally opposite surfaces of thelimb. For clarity only the TD for limbs 163 and 164 are shown, but theother limbs are analogous. Each of the four limbs 161, 162, 163, 164 hasa longitudinal thickness “T” of 1.5-2.0 mm, and a transversely extendinglength “L” of 9-12 mm between transversely opposite folds 171, 172, 173,and between folds 171 and 173 and the adjacent edges of troughs 181,183. Each of the four limbs 161, 162, 163, 164 has a width “W” of 9-12mm in the width direction as indicated in FIG. 3. The width W of thefolds 171, 172, 173 decreases toward the head 11. The two limbs 161, 162closest to the handle 12 both have a width W of ca. 11.5 mm. The twolimbs 163 and 164 progressively closer to the head 11 have respectivewidths 11.2 and 10.2 mm. As viewed in the longitudinal direction thelimbs 161, 162, 163, 164 have a generally rectangular shape with roundedcorners.

The three troughs 181, 182, 183 each have a transverse depth “D” of 6-9mm. The measurement of the depths of the troughs 181, 182, 183 is seenmost clearly in FIG. 5. The depth D1 of trough 181 is measured from themid-point of line L1-L2, constructed between the outermost curve of theadjacent fold 172 and the adjacent edge 166 of the trough 181 to thebottom of the trough. The depth D3 of trough 182 is measured from themid-point of line L4-L5, constructed between the outermost curves of theadjacent folds 171, 173 to the bottom of the trough 182. The depth D2 oftrough 183 is measured from the mid-point of line L2-L3, constructedbetween the outermost curve of the adjacent fold 172 and the adjacentedge 167 of the trough 183, i.e. the convex outer inflexion point of thelimb 164 to the bottom of the trough 183. The constructed lines L1-L2,L2-L3 and L4-L5 each contact the convex inflexion points of the folds171, 172, 173.

The three troughs vary in depth. The trough 183 closest to the head 11has a depth D2 of ca. 7.0 mm, the middle trough 182 has a depth D3 ofca. 10.0 mm, and the trough 181 closest to the grip handle 12 has adepth D1 ca. 8.0 mm, i.e. the middle trough 182 is the deepest.

The three troughs 181, 182, 183 have a longitudinal breadth “b” of 1-2mm for at least 60% of the depth of each trough 181, 182, 183. Thelongitudinal breadth “b” tapers, narrowing toward the bottom of thetrough 181, 182, 183, and being 1-1.5 mm for at least 60% of the depthof the trough 181, 182, 183.

Each of the folds 171, 172, 173 is externally in the form of an arc of acircle with an outer radius of curvature of 2.25-2.35 mm. The thicknessof the folds measured in the radial direction of this circle is 1.5-2.0mm.

The plastic material part 10 is made of the polypropylene plasticsmaterial 100-GA04 supplied by Ineos.

FIGS. 2 and 4 show a toothbrush of the invention overall 20 includingthermoplastic elastomer material 21 that extends over part of the griphandle 12 to enhance a user's grip.

Each trough 181, 182, 183 contains thermoplastic elastomer material 21seen in FIGS. 2 and 4. The thermoplastic elastomer material is thecommercially available material TF7 GST or TF7 GSN supplied by Kraiburgand having a ShoreA hardness 60-70. The thermoplastic elastomer material21 is bonded to the plastic material of the limbs 161, 162, 163, 164.The thermoplastic elastomer material 21 occupies at least 75% of thetransverse depth “D” and at least 75% of the width “W” of each trough181, 182, 183.

At each longitudinal end of the undulating region 16 there is an endtrough 184, 185 in the plastics material, which also containthermoplastic elastomer material 21. These end troughs 184, 185 can actas a force-absorbing buffer between the neck region 13 at onelongitudinal end of the undulating region 16, and the grip handle 12 atthe other. The end trough 184 between the undulating region 16 and thegrip handle 12 has a transverse depth “E1” of 5.5-6.5 mm, preferablyca.6 mm, measured as shown in FIG. 5 between a longitudinal projectionof the surface of the grip handle 12 and the opposite surface of limb161, and has a longitudinal breadth “b” of 1-2 mm for all of its depth.The end trough 185 between the undulating region 16 and the neck region13 has a transverse depth “E2” of ca. 6.0 mm, measured as shown in FIG.5 between a longitudinal projection of the surface of the neck region 13and the opposite surface of limb 164, and has a longitudinal breadth “b”of 1-2 mm for all of its depth.

As seen in FIGS. 2 and 4 these end troughs 184, 185 also contain thethermoplastic elastomer material of ShoreA hardness 60-70 bonded to theplastic material of the limbs 161, 164 and of respectively the griphandle 12 and the neck region 13, and occupying at least 75% of thetransverse depth E1, E2 and at least 60% of the width of the end troughs184, 185.

The toothbrush 20 of the invention also includes a flexible link 30(overall) seen fully in FIGS. 2 and 4 situated longitudinally betweenthe undulating region 16 and the toothbrush head 11. This flexible link30 is situated in the neck region 13 thereby dividing the neck region 13into two longitudinally separate parts 133, 134 on each longitudinalside of the flexible link 30, a first part 133 being closer to the griphandle 12, the second part 134 being closer to the head 11.

The flexible link 30 comprises a plastics material part 31 seen clearlyin FIGS. 1 and 3, integral with the neck region 13, which is transverslyand widthways thinned relative to longitudinally immediately adjacentparts of the neck region 13. This part 31 is in the form of alongitudinally extending spine of plastics material having alongitudinal dimension of 1-2 mm, a widthways dimension of 2-3 mm, and atransverse dimension of 1.5-2.5 mm. The cross section of the part 31 cutacross the longitudinal direction is approximately circular.

The relative longitudinal proportions of the first part 132: second part133, are approximately 8.25:1. These proportions are based respectivelyas the length of the first part 132 being the longitudinal distance fromthe edge 185A of the end trough 185 closest to the head 11, to the endof the thinned part 31 closest to the grip handle 12 (this distance isca. 28 mm), and the length of the second part 133 as the longitudinaldistance from the end of the thinned part 31 closest to the head 11, tothe point 131 where the neck region 13 begins to widen to form the head11, this distance is ca. 3.5 mm. As seen in FIGS. 2 and 4 the thinnedpart 31 is surrounded around all of its transversely- andwidthways-facing surfaces by thermoplastic elastomer material 32 havinga spherical shape, with a spherical diameter of 6-7 mm. Thethermoplastic material 32 is the same thermoplastic elastomer material21 that is situated in the troughs 181, 182, 183, 184, 185.

The first part 133 of the neck region between the flexible link 30 andthe undulating region 16 is constructed such that under the forcesencountered during tooth brushing this first part 133 remains rigidrelative to the flexibility of the flexible link 30 and the undulatingregion 16. This is achieved by the first part 133 having a transversethickness “T” of at least 3.5 mm, being ca. 5 mm at the point 131 wherethe part 133 meets the undulating region 16 and 4-4.5 mm at the end ofthe first part 133 adjacent to the link 30. The first part 133 has awidthways width of at least 5 mm, being a width of ca. 9 mm at the point131, and ca. 5.9 mm at the end of the first part 133 adjacent to thelink 30.

In various places in the plastic material part 10, are apertures andmoulding channels such as 40 into and through which the elastomermaterial 21 can flow from a single or multiple injection points to reachother parts of the plastic material part 10 of the toothbrush 20.

A toothbrush according to the above example was subjected to bendingforces applied to the head and the stresses at various points in thetoothbrush were measured. It was found that the structure and dimensionsof the toothbrush described in the above example showed an acceptabledegree of deformation in response to tooth brushing pressures. Thistoothbrush showed more deformation in its S-bend undulating region thanin its brush head region thereby reducing potential breaking stress inthe flexible link 30 between the head and handle. The deformation in theS-bend undulating region during use was greater than in the S-bendregion disclosed in the prior references mentioned above, withdeformation concentrated in the limb 164 and fold 173 closest to thetoothbrush head 11.

1. A toothbrush comprising a head and a grip handle integrally made of aplastics material and arranged along a head-handle longitudinaldirection, with a neck region between the grip handle and the head, withbristles projecting from the head in a transverse direction relative tothis longitudinal direction, the toothbrush having a width directionperpendicular to the longitudinal direction and to the transversedirection, wherein longitudinally between the neck region and the griphandle is a an undulating region, comprising limbs extending in thetransverse direction and integrally linked by folds with troughs betweenthe limbs, the troughs between the limbs having a transverse depthdirection and containing a thermoplastic elastomer material bonded tothe plastic material of said limbs, wherein, the thermoplastic elastomermaterial has a ShoreA hardness of 60-70.
 2. A toothbrush according toclaim 1, wherein there are four limbs.
 3. A toothbrush according toclaim 1, wherein the thermoplastic elastomer material occupies at least60% of the transverse depth “D” and at least 60% of the width of atleast one trough.
 4. A toothbrush according to claim 1, wherein thetransverse directions of longitudinally adjacent pairs of limbs arealigned at an angle of 0-15° to each other, each of the four limbshaving a longitudinal thickness “T” of 1.2-2.2 mm, and a transverselyextending length “L” of 9-13 mm between transversely opposite folds, anda width “W” of 9-14 mm in the width direction, the four limbs defininglongitudinally between longitudinally adjacent pairs of the limbs threetroughs each with a transverse depth “D” of 6-11 mm, a longitudinalbreadth “B” of 1-2 mm for at least 60% of the lower depth of the trough,each trough containing the thermoplastic elastomer.
 5. A toothbrushaccording to claim 1, wherein at each longitudinal end of the undulatingregion there is an end trough in the plastics material, bounded on onelongitudinal side by an adjacent limb and on the other longitudinal sideby an adjacent surface of the grip handle or head, the end troughs alsocontaining the thermoplastic elastomer material.
 6. A toothbrushaccording to claim 1, wherein the neck region is flattened in thetransverse direction.
 7. A toothbrush according to claim 1, whereinwhich also includes a flexible link situated longitudinally between theundulating region and the toothbrush head.
 8. A toothbrush according toclaim 7, wherein the flexible link is situated in the neck regionthereby dividing the neck region into two longitudinally separate parts,one on each longitudinal side of the flexible link, being a first partcloser to the grip handle and a second part closer to the head.
 9. Atoothbrush according to claim 8, wherein the relative longitudinalproportions of the first part: second part are in the range 8.5-8.0:1.10. A toothbrush according to claim 7, wherein the flexible linkcomprises a part, integral with the neck region, which is transverselyand/or widthways thinned relative to longitudinally immediately adjacentparts of the neck region.
 11. A toothbrush according to claim 10,wherein the part which is transversly and/or widthways thinned issurrounded around all of its transversely- and widthways-facing surfacesby a thermoplastic elastomer material.
 12. A toothbrush according toclaim 11, wherein the thermoplastic elastomer which surrounds thethinned part has a spherical symmetry.
 13. A toothbrush according toclaim 11, wherein the end of the flexible link closest to the undulatingregion is located within 30 mm of the end of the undulating regionclosest to the undulating region.
 14. A toothbrush according to claim11, wherein the part of the neck region between the flexible link andthe undulating region is constructed such that under the forcesencountered during tooth brushing this part remains rigid relative tothe flexibility of the flexible link and the undulating region.
 15. Atoothbrush according to claim 11, wherein the plastic material has amodulus of elasticity of at least about 500 Mpa, and is a polyamide orpolypropylene.
 16. A toothbrush according to claim 11, wherein thethermoplastic elastomer material is a styrene-based thermoplasticelastomer.